In a series of letters to the 10-, 25-, 50- and 65-year-old versions of himself, Branson shares what he wishes he had known at different stages of his career.

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Virgin Group founder Richard Branson

"You won't always succeed," the self-made billionaires writes to his 25-year-old self. "In fact, you will fail time and time again. That's OK though, because failure is an inevitable part of every personal and entrepreneurial journey."

Nobody gets it right the first time, he emphasizes. What matters is that you "continue to take chances," he says. "In the future how 'lucky' you are in business will be determined by how willing you are to take calculated risks."

After years of calculated risks, Branson had, by age 50, launched hundreds of companies and been a billionaire for nearly a decade. "On the business front, you may feel like you've achieved just about all there is to achieve," he writes to the middle-aged version of himself. "But let me tell you, there are so many more great things to come. …

"The future will be so bright, if you continue to look for opportunities where others see challenges."

To this day, Branson doesn't feel like he's "made it." "The way I see it, life is all about striving and growing,"he says. "I never want to have made it; I want to continue making it!"